Blower motor
Q I’m trying to diagnose a fault on a heater blower motor on a 2017 VW Touareg (engine code CVVA), type: 7P6 2RJ. The fault is that when the fan runs at high speed, it cuts out after running for about 30 secs. When at medium speed, the fan works OK. It is likely that I need to replace the fan motor but that’s not the point. I am trying to prove that the fan is faulty but can’t seem to find anything on the web that shows me how to test it.
The fan is a 3-wire fan. It has a permanent live and a ground, both thick wires. There is a third thinner wire which I am sure comes from the aircon controller from the centre of the dash.
I think the fan is controlled via the thin wire by a PWM, pulse width modulator signal, and this signal controls the speed of the fan. What I want to do it test the signal and see it change when the fan fails to run before I replace it.
I don’t have an oscilloscope but do have VCDS and a very good multimeter. Any help would be grateful.
Shabaz Mohammed A The blower motor incorporates the control board which is directed by the pulse feed from the third wire. If using VW diagnostic equipment, you would probably expect to see the fault code 0258 control module for air blower B10BB 04 Internal system fault. Or possibly 0204 control unit for blower motor. This would confirm that the motor was as fault. As these motors are around £360 I can see why you would want to confirm this before replacing it.
The third wire sends a ‘Discreet signal’. This is a voltage signal which is sent via a normal cable and can only be tested using an oscilloscope, the basic operation of the fan is that the heating and ventilation system sends the pulse signal to the fan where it is received by an NPN Transistor incorporated in the fan control circuit. This dictates the speed of the fan by directing the voltage to the negative side of the system to adjust the speed of the fan.
As this pulse rate is normally 2-4 pulses per fan rotation, this can only be checked using an oscilloscope as the speeds of the pulses would be unmeasurable using a test light or meter.